Hydrogen Fuel Cells - Basic Principles

Basic principles of the oxygen-hydrogen fuel cell... 

Cells operating with hydrogen as the fuel are the simplest such devices, and serve to illustrate basic principles. Schematic diagrams of hydrogen/oxygen cells appear in Fig. 13.6. When the electrolyte is acidic [Fig. 13.6(a)], the half-cell reaction occurring at the hydrogen electrode (anode) is ... 

Equation (3) and (4) mean that the supply of the energetic e is needed to split water. This is the basic principle of water-electrolysis. The PEMFC is just the reverse operation of the SPE. Hydrogen fuel is decomposed into 2e and 2H+ by the catalytic cathode. The protons pass through the solid polymer (electrolyte) and arrive at the anode (A) to react with the electrons and the supplied oxygen. Then, water is produced. The electrons come to A via the external resistance. This fuel cell generates, ideally, about 1 V-direct current power. A stack of the cells is constructed to give the output power with, for example, 25 kW, which is set together to drive the vehicles. 

The basic structure and principle of all fuel cells is similar the cell consists of two electrodes which are separated by an electrolyte. The electrodes are connected through an external circuit. The electrodes are exposed to gas or liquid flows to supply fuel and oxidant (for instance hydrogen and oxygen). The electrodes have to be gas or liquid permeable and therefore possess a porous structure. The electrolyte should have a gas permeability as low as possible. For fuel cells with an acid electrolyte, hydrogen is oxidized at the negative electrode (the anode) according to the following equation. The protons formed enter the electrolyte and are transported to the cathode ... 

At present, most of the work toward building methanol fuel cells relies on technical and design principles, developed previously for polymer electrolyte membrane fuel cells. In both kinds of fuel cells, it is common to use platinum-ruthenium catalysts at the anode and a catalyst of pure platinum at the cathode. In the direct methanol fuel cells, the membrane commonly used is of the same type as in the hydrogen-oxygen fuel cells. The basic differences between these versions are discussed in Section 19.7. 

BP) acts, on the one hand, as a positive cathode for one cell and, on the other, as a negative anode for the next cell. A schematic diagram of the fuel cell configuration and basic operating principles of a hydrogen-fed PEMFC and a DMFC are shown in Figure 5.1. 

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